The present invention relates to an x-ray diffractometer for measuring the x-ray diffraction pattern of a polycrystalline sample, a powder sample or the like.
In a qualitative or quantitative analysis of a powder sample or the like, or in an analysis of a crystalline structure, there is generally used a so-called goniometer method in which, while an x-ray beam having a suitable angle of aperture is irradiated to a sample placed at the center of a goniometer and an x-ray detector is rotated around the sample, there is measured the intensity of x-rays diffracted by the sample. In such a goniometer method, there is generally used a so-called .theta.-2.theta. interlock scan method in which, when the angle of the sample with respect to a zero angle direction in which the x-ray generator and the goniometer center (i.e., the sample center) are connected to each other, is defined as .theta., the sample and the x-ray detector are interlockingly scanned around the same rotational axis such that the angle of the x-ray detector with respect to the zero angle direction is always maintained at 2.theta..
According to the .theta.-2.theta. interlock scan method, an analysis result with high precision can be obtained by a simple operation for a homogeneous sample. However, for an insufficiently mixed sample, a powder sample in which individual crystalline grains are large, a sample having an uneven surface such as metal in which crystalline grains are coarse due to heat treatment, or the like, the intensity of x-ray deffracted measured by an x-ray detector is reduced, according to the reduction in the number of crystalline grains which contribute to the generation of diffracted rays in one direction; so that this .theta.-2.theta. interlock scan method is disadvantageously liable to contain errors in the measurement result.
To solve such a problem, there has conventionally been proposed a sample vibration-type x-ray diffractometer in which, during the .theta.-2.theta. interlock scan, the sample is rotationally vibrated (swung), on the same axis as the rotational axis for the .theta. scan, at an angular speed greater than the scan speed, thereby to increase the number of crystalline grains which contribute to the generation of diffracted rays at each angular position of the sample.
FIG. 5 shows an example of a conventional sample vibration-type x-ray diffractometer of the type above-mentioned. X-rays 52 generated by an x-ray tube 51 are irradiated, as suitably limited in diffusion by a divergence slit 53, to a sample 54 obtained by hardening a powder sample in the form of a plate.
The sample 54 as supported by a sample placing stand 55, is placed on a sample table 56. The sample table 56 is arranged to be rotated around a rotational axis 57 by a motor (not shown) such that the angle .theta. of the sample 54 with respect to the irradiated x-rays 52 varies with the passage of time. This operation is hereinafter referred to as .theta.-scan.
X-rays 58 diffracted by the sample 54, are to be detected by an x-ray detector 60 through a detecting slit 59. The detecting slit 59 and the x-ray detector 60 are to be rotated also around the rotational axis 57 by a motor (not shown), and the rotational position is controlled such that the angle of the x-ray detector 60 with respect to the irradiated x-rays 52 is always twice the angle .theta. of the sample 54 with respect to the x-rays 52, the angle .theta. varying from time to time. More specifically, in association with the .theta. scan of the sample 54, the detecting slit 59 and the x-ray detector 60 are scanned at an angular speed which is double the angular speed in the .theta. scan (hereinafter referred to as 2.theta. scan).
In addition to the .theta. scan by the rotation of the sample table 56, the sample 54 is subjected to rotational vibration around the rotational axis 57 by the following mechanism.
The sample placing stand 55 for supporting the sample 54, is supported by the sample table 56 in a manner rotatable around the rotational axis 57 and has, in a unitary structure, a lever 61. On the other hand, a motor 63 having the output shaft to which an eccentric cam 62 is secured, is mounted on the sample table 56, and the lever 61 of the sample placing stand 55 is biased by a spring 64, causing the lever 61 to be normally brought in close contact with the outer peripheral surface of the eccentric cam 62. The motor 63 is rotationally driven at an angular speed greater than that of the motor for rotating the sample table 56 such that the sample 54 is subjected to the .theta. scan. The rotation of the motor 63 causes the sample placing stand 55 to be rotationally vibrated on the sample table 56 around the rotational axis 57 as shown by the arrow in FIG. 5. Thus, the sample 54 is subjected not only to the .theta. scan, but also to a rotational vibration at an angular speed faster than that for the .theta. scan.
According to such a sample vibration-type x-ray diffractometer of prior art, it is required to dispose, on the sample table, a drive mechanism for rotationally vibrating a sample, in addition to the drive mechanism for .theta.-2.theta. interlock scan. However, the sample holding members such as the sample table and the sample placing stand are generally replaced according to the shape and type of a sample. Accordingly, it is required in such a conventional diffractometer to mount a drive mechanism for rotationally vibrating a sample on each of all the sample tables to be used. This increases the cost of a sample table. Further, it is rather difficult to install such a drive mechanism for rotational vibration in a limited space on the sample table.